1. Field of the Invention
The present invention relates to communications, and more particularly, to an arrangement of repeaters for communications on a bi-directional medium. The arrangement is suited for communications over a power line.
2. Description of the Related Art
Many types of communications media are characterized by a single signal medium whose physical continuity cannot be interrupted. There are also communications transducers that are totally bi-directional, as opposed to being omni-directional, or have very limited directionality. Examples include energized electrical power wires, gasses and fluids confined to pipes, and certain optical media.
For example, for power line communications, a signal is coupled to a wire in a non-directional manner, that is, the signal may propagate in both directions along a wire. Often, one direction is an intended direction and the other direction is unintended.
At some distance from a signal source of a signal, a signal to noise ratio will deteriorate to a point that a repeater is necessary to allow data represented by the signal to be conveyed at reasonable quality beyond that point. For a full duplex modem that is continuously transmitting, a receiver can receive signals from both directions, and the possibility exists for signals propagating in an unintended direction to interfere with intended signals.
If multiple frequency bands are available, then the repeater may receive at one frequency and retransmit at another frequency. However, even this arrangement does not ensure immunity from interference, especially if the level of the intended signal is similar to that of the unintended signal, due to similar attenuations between the respective transmitters and the receiver.